slotted flaps

[Bootlegger]

  I keep reading about these flaps and am curious as to how they work.  How do you set them up, and any other info that y'all can share will be greatly appreciated,  Thanks..

[Will Hinton]

Hi Gil, I suspect you're thinking about Wesley Dick's Velvet.  He has built several and I think his new version will be electric for this year.  Try a search for him and the Velvet and see what you can find.
I've seen a couple of them fly and they look quite good.

[Tim Wescott]

Just go to the main forum page (the one that lists all the various fora) and type "Velvet" into the search bar (upper right region of the screen).  You get lots of hits -- like this one.

"How do they work aerodynamically" is, I think, a different question than "are they worth it for us".  Just reading about it I certainly see enthusiasm, but looking at Nat's winners I see a lot of simple, unslotted flaps.

[Ken Culbertson]

  I keep reading about these flaps and am curious as to how they work.  How do you set them up, and any other info that y'all can share will be greatly appreciated,  Thanks..

This got my curiosity up as well so I read up on the Velvet.  Pure genius.  One thing I did not get from the research was: Is the first slot in the smaller "flap" sealed?  If it is than I think Wesley has come as close to making a true bidirectional slotted flap as possible. I would love to see some wind tunnel tests.

Ken

[Tim Wescott]

This got my curiosity up as well so I read up on the Velvet.  Pure genius.  One thing I did not get from the research was: Is the first slot in the smaller "flap" sealed?  If it is than I think Wesley has come as close to making a true bidirectional slotted flap as possible. I would love to see some wind tunnel tests.

Ken

Hey Ken -- look at the pictures in some of the threads.  The answer is, no, that first slat is clearly hanging out in the breeze, directing the airflow over the second slat.  It does, to my casually-educated eye, look like it may actually be acting like a slotted flap, and given the sizes of the gaps, it may actually be consistent (the reason you're urged to seal the hinge lines on the typical simple stunter is for consistency -- you can get consistent behavior from a flap with narrow gaps and insane levels of precision, or big gaps, or with sealed gaps).

[Ken Culbertson]

Hey Ken -- look at the pictures in some of the threads.  The answer is, no, that first slat is clearly hanging out in the breeze, directing the airflow over the second slat.  It does, to my casually-educated eye, look like it may actually be acting like a slotted flap, and given the sizes of the gaps, it may actually be consistent (the reason you're urged to seal the hinge lines on the typical simple stunter is for consistency -- you can get consistent behavior from a flap with narrow gaps and insane levels of precision, or big gaps, or with sealed gaps).

I have a some experience with slotted/fowler flaps in the Air Force with STOL aircraft.  Everything I knew told me that the slot should open on the underside of the wing ahead of the wing T/E which precludes bi-directional.  In the case of Fowler, the flap will either move back without creating the slot to increase wing area then drop down creating the slot or drop down creating the slot then move back as it drops.  Doubles do it twice.  What I see on the Velvet is neither Slotted or Fowler as they are defined HOWEVER, they do have slots and they do appear to work.  I almost bought one of these last spring.  It looked very much like a Velvet but was smaller.  I think it may have belonged to Tom Farmer at one point.  I needed a PA ship to practice with but I didn't have a Briggs & Stratton engine to put in it  -- HEAVY -- so I passed.
The reason I said I would like to see wind tunnel tests is that I can't quite grasp why it is producing better lift without the wing overlapping the slot.  This is the kind of stuff that turns my brain into a pretzel!

ken

[Tim Wescott]

The reason I said I would like to see wind tunnel tests is that I can't quite grasp why it is producing better lift without the wing overlapping the slot.  This is the kind of stuff that turns my brain into a pretzel!

ken

Given that simple flaps seem to work perfectly well, and will turn a well-trimmed stunter on a dime with no hint of stall, I'm not sure that the Velvet flap is acting as a slotted flap.  It could just be that it's a very complicated way of getting essentially the same aerodynamic effect as a simple flap, but with a lot of mechanical 'woo'.

OTOH, it could be that having a lot of overhang on a slotted flap is good, but not necessary to get at least some positive result.  I landed head-first on the rear window of a car during rush hour in the mid 1980's commuting home from school, and haven't been able to work out computational fluid dynamics problems in my head since*.

Speaking from personal experience, I've flown a heavy Ringmaster in the pattern, so I know what a stall feels like out at the end of the line.  I've also had a couple of planes that will turn fast enough to burn off a lot of speed in a corner, and the feeling is not like a stall -- it's a lot more consistent with scrubbing off speed due to induced drag (and that's consistent with high aspect ratio stunters being able to corner better, although I haven't had that experience).

I really don't think that flaps, done the way we do them, are particularly high-lift devices.  I think they mostly increase scores by letting the plane groove better in the rounds and level -- and in fact, Igor Burger's logarithmic flap mechanism changes the flap/elevator ratio with deflection, essentially letting the flaps max out in the corners for more "turn" without more lift.  And Igor Burger seems to be a reasonably good pilot.

* Not that I ever could before, but definitely not since!

[John Watson]

Anyone tried this effect on a carrier plane. They resemble the flaps on STOL
 A/C...…..

[frank williams]

I would recommend the thread down below int the "Stunt Design" section titled "flap efficiency ...."  Its pretty recent.

[EddyR]

 Back in the late 1950's and early 1960's slotted flaps were seen on a lot of stunt planes. I saw a few at the 1957 Nats. The slots went the entire length of the flap and were 1.5-2" wide. The pivot point was such that the flap front would move above or below the trailing edge. I think it was a way to get more originality points. I the slot was 3/8 to 1/2" deep.
  One of the mods to the Fierce Arrow was to make the elevator slotted. I tried it on mine.
Ed

[Dan McEntee]

  Wasn't there a feature article on the Velvet in Stunt News? I think Wes wrote up a series of articles on it and the flap system? I think there was also an article in StuntNews or Model Aviation on it when he donated the original to the AMA Museum?? The old memory bank is tired and just can't lock in!
   Type at you later,
    Dan McEntee

[john e. holliday]

Did a search using  velvet  for key word.  Third item that came up: April 2015 PAMPA Stunt News  Velvet consrtuction Pt 1.


Did not go down any further.

[EddyR]

  above I mentioned slotted flaps models in the 1950-60's      I thought I remembered the  Ballerina as having slotted flaps. It took awhile to find this but here it is at the 1961 Nats

 

[Ken Culbertson]

  above I mentioned slotted flaps models in the 1950-60's      I thought I remembered the  Ballerina as having slotted flaps. It took awhile to find this but here it is at the 1961 Nats

 

This plane was the inspiration for my Sandpiper design.  I loved it's looks but I don't remember it having slotted flaps as we are discussing them here, I think it had tubular hinges which probably creates a slot.  I may be wrong, I was 14 and had hair at the time.

Ken

[Steve Helmick]

From the Ballerina picture posted, it looks to me more like an effort at aerodynamic balancing than slotted flaps. Probably not a good idea. Less flap area and a better control system (bigger BC, longer horns) would likely work more predictably.  Steve

[RogerGreene]

I believe that the Ballerina's flaps are hinged by using tubing lengths attached to the wing trailing edge and flap leading edge like a door hinge and not slotted flaps.

[frank williams]

This offset hinge line works well on a stunt ship.

[EddyR]

  The slotted hinges I remember hinged at the back of the flap slot.  When deflected down it raised the leading edge of the flap above the top trailing edge. You could see through the slot.
  I saw this same thing on a modern stunner at Huntersville a few years ago. I believe it was on a Imported semi arf . Modeler was from Miami area. Maybe early version of the Shark. I do have digital pictures in my archive.
  EddyR

[frank williams]

Just for fun

[john e. holliday]

Frank I remember that design was supposed to be a trainer.